package com.hall.util;

public class IdWorker {
	// 下面两个每个5位，加起来就是10位的工作机器id
	private long workerId; // 工作id
	private long datacenterId; // 数据id
	// 12位的序列号
	private long sequence;

	public IdWorker(long workerId, long datacenterId, long sequence) {
		// sanity check for workerId
		if (workerId > maxWorkerId || workerId < 0) {
			throw new IllegalArgumentException(String.format(
					"worker Id can't be greater than %d or less than 0",
					maxWorkerId));
		}
		if (datacenterId > maxDatacenterId || datacenterId < 0) {
			throw new IllegalArgumentException(String.format(
					"datacenter Id can't be greater than %d or less than 0",
					maxDatacenterId));
		}
		System.out
				.printf("worker starting. timestamp left shift %d, datacenter id bits %d, worker id bits %d, sequence bits %d, workerid %d",
						timestampLeftShift, datacenterIdBits, workerIdBits,
						sequenceBits, workerId);

		this.workerId = workerId;
		this.datacenterId = datacenterId;
		this.sequence = sequence;
	}

	// 初始时间戳
	private long twepoch = 1288834974657L;

	// 长度为5位
	private long workerIdBits = 5L;
	private long datacenterIdBits = 5L;
	// 最大值
	private long maxWorkerId = -1L ^ (-1L << workerIdBits);
	private long maxDatacenterId = -1L ^ (-1L << datacenterIdBits);
	// 序列号id长度
	private long sequenceBits = 12L;
	// 序列号最大值
	private long sequenceMask = -1L ^ (-1L << sequenceBits);

	// 工作id需要左移的位数，12位
	private long workerIdShift = sequenceBits;
	// 数据id需要左移位数 12+5=17位
	private long datacenterIdShift = sequenceBits + workerIdBits;
	// 时间戳需要左移位数 12+5+5=22位
	private long timestampLeftShift = sequenceBits + workerIdBits
			+ datacenterIdBits;

	// 上次时间戳，初始值为负数
	private long lastTimestamp = -1L;

	public long getWorkerId() {
		return workerId;
	}

	public long getDatacenterId() {
		return datacenterId;
	}

	public long getTimestamp() {
		return System.currentTimeMillis();
	}

	// 下一个ID生成算法
	public synchronized long nextId() {
		long timestamp = timeGen();

		// 获取当前时间戳如果小于上次时间戳，则表示时间戳获取出现异常
		if (timestamp < lastTimestamp) {
			System.err.printf(
					"clock is moving backwards.  Rejecting requests until %d.",
					lastTimestamp);
			throw new RuntimeException(
					String.format(
							"Clock moved backwards.  Refusing to generate id for %d milliseconds",
							lastTimestamp - timestamp));
		}

		// 获取当前时间戳如果等于上次时间戳（同一毫秒内），则在序列号加一；否则序列号赋值为0，从0开始。
		if (lastTimestamp == timestamp) {
			sequence = (sequence + 1) & sequenceMask;
			if (sequence == 0) {
				timestamp = tilNextMillis(lastTimestamp);
			}
		} else {
			sequence = 0;
		}

		// 将上次时间戳值刷新
		lastTimestamp = timestamp;

		/**
		 * 返回结果： (timestamp - twepoch) << timestampLeftShift)
		 * 表示将时间戳减去初始时间戳，再左移相应位数 (datacenterId << datacenterIdShift)
		 * 表示将数据id左移相应位数 (workerId << workerIdShift) 表示将工作id左移相应位数 |
		 * 是按位或运算符，例如：x | y，只有当x，y都为0的时候结果才为0，其它情况结果都为1。
		 * 因为个部分只有相应位上的值有意义，其它位上都是0，所以将各部分的值进行 | 运算就能得到最终拼接好的id
		 */
		return ((timestamp - twepoch) << timestampLeftShift)
				| (datacenterId << datacenterIdShift)
				| (workerId << workerIdShift) | sequence;
	}

	// 获取时间戳，并与上次时间戳比较
	private long tilNextMillis(long lastTimestamp) {
		long timestamp = timeGen();
		while (timestamp <= lastTimestamp) {
			timestamp = timeGen();
		}
		return timestamp;
	}

	// 获取系统时间戳
	private long timeGen() {
		return System.currentTimeMillis();
	}

}
